Size mismatch: A crucial factor for generating a spin-glass insulator in manganites

Abstract

The structural, electronic, and magnetic properties of the highly mismatched perovskite oxides, ${\mathrm{Th}}_{0.35}{A}_{0.65}{\mathrm{MnO}}_{3},$ where A is for the alkaline earth divalent cations (Ca, Ba, Sr), which are all characterized by the same large tolerance factor $(t=0.934),$ have been investigated by using electron microscopy, electrical resistivity, magnetic susceptibility, and magnetization. It is clearly established that a transition from ferromagnetic metallic towards spin-glass insulator samples is induced as the A-site cationic size mismatch is increased. Moreover, the magnetoresistance (MR) properties of these manganites are strongly reduced for the spin-glass insulators, demonstrating that the A-site cationic disorder is detrimental for the colossal MR properties. Based on these results, a new electronic and magnetic diagram is established that shows that the A-site disorder, rather than the A-site average cationic size (or t) is the relevant factor for generating spin-glass insulating manganites.